Polyimide composition

ABSTRACT

A preparation method of separation membrane is provided. First, a polyimide composition including a dissolvable polyimide, a crosslinking agent, and a solvent is provided. The dissolvable polyimide is represented by formula 1: 
     
       
         
         
             
             
         
       
         
         
           
             wherein B is a tetravalent organic group derived from a tetracarboxylic dianhydride containing aromatic group, A is a divalent organic group derived from a diamine containing aromatic group, A′ is a divalent organic group derived from a diamine containing aromatic group and carboxylic acid group, and 0.1≤X≤0.9. The crosslinking agent is an aziridine crosslinking agent, an isocyanate crosslinking agent, an epoxy crosslinking agent, a diamine crosslinking agent, or a triamine crosslinking agent. A crosslinking process is performed on the polyimide composition. The polyimide composition which has been subjected to the crosslinking process is coated on a substrate to form a polyimide membrane. A dry phase inversion process is performed on the polyimide membrane.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of and claims the prioritybenefit of U.S. patent application Ser. No. 15/472,272, filed on Mar.29, 2017, now allowed, which claims the priority benefit of Taiwanapplication serial no. 105111004, filed on Apr. 8, 2016. The entirety ofeach of the above-mentioned patent applications is hereby incorporatedby reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention generally relates to a composition, andparticularly to a polyimide composition, and a preparation method ofseparation membrane using the polyimide composition.

2. Description of Related Art

Membrane separation processes are a technology that becomes increasinglyimportant in the field of separation science, and find wide use in theseparation of gas or liquid components, for example gas separation,pervaporation (PV), vapour permeate (VP) or liquid filtration. In aconventional membrane separation process, the film is generally made ofpolytetrafluoroethylene (PTFE), ceramic or glass fiber. Although thePTFE, ceramic or glass fiber separation membranes all have goodresistance to high-polarity solvents, the processability of the ceramicor glass fiber separation membranes is poor. Moreover, in the prior art,the PTFE, ceramic or glass fiber separation membrane can only be used inmicrofiltration (MF). Therefore, one objective in urgent need fordevelopment in the field is to prepare a separation membrane with goodresistance to high-polarity solvents and processability that can be usedin PV and VP.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a polyimidecomposition that is useful in a preparation method of separationmembrane, and a separation membrane with good resistance tohigh-polarity solvent and processability that can be used in PV and VPcan be prepared through the preparation method.

The preparation method of separation membrane according to the presentinvention comprises the following steps. First, a polyimide compositionincluding a dissolvable polyimide, a crosslinking agent, and a solventis provided. The dissolvable polyimide is represented by formula 1below:

where B is a tetravalent organic group derived from a tetracarboxylicdianhydride containing aromatic group, A is a divalent organic groupderived from a diamine containing aromatic group, A′ is a divalentorganic group derived from a diamine containing aromatic group andcarboxylic acid group, and 0.1≤X≤0.9. The crosslinking agent is anaziridine crosslinking agent, an isocyanate crosslinking agent, an epoxycrosslinking agent, a diamine crosslinking agent, or a triaminecrosslinking agent. A crosslinking process is performed on the polyimidecomposition. The polyimide composition which has been subjected to thecrosslinking process is coated on a substrate to form a polyimidemembrane. A dry phase inversion process is performed on the polyimidemembrane.

In an embodiment of the present invention, based on the total weight ofthe polyimide composition, the content of the dissolvable polyimide is 5to 25 wt %, and the content of the crosslinking agent is 1 to 15 wt %.

In an embodiment of the present invention, in formula 1, B is

In an embodiment of the present invention, in formula 1, B is

A is

and A′ is

In an embodiment of the present invention, the aziridine crosslinkingagent may include

In an embodiment of the present invention, the duration of thecrosslinking process is from 1 to 8 hours, and the temperature of thecrosslinking process is in the range of 15 to 100° C.

In an embodiment of the present invention, the thickness of thepolyimide membrane is in the range of 1 to 50 μm.

The polyimide composition of the present invention includes adissolvable polyimide, a crosslinking agent, and a solvent. Thedissolvable polyimide is represented by formula 1:

where B is a tetravalent organic group derived from a tetracarboxylicdianhydride containing aromatic group, A is a divalent organic groupderived from a diamine containing aromatic group, A′ is a divalentorganic group derived from a diamine containing aromatic group andcarboxylic acid group, and 0.1≤X≤0.9. The crosslinking agent is anaziridine crosslinking agent, an isocyanate crosslinking agent, an epoxycrosslinking agent, a diamine crosslinking agent, or a triaminecrosslinking agent.

In an embodiment of the present invention, in formula 1, B is

In an embodiment of the present invention, in formula 1, B is

A is

and A′ is

In an embodiment of the present invention, the aziridine crosslinkingagent may include:

In an embodiment of the present invention, based on the total weight ofthe polyimide composition, the content of the dissolvable polyimide is 5to 25 wt %, and the content of the crosslinking agent is 1 to 15 wt %.

Based on the above description, the polyimide composition of the presentinvention includes a dissolvable polyimide, a crosslinking agent and asolvent, and the dissolvable polyimide contains a specific ratio of adivalent organic group derived from a diamine containing aromatic groupand a divalent organic group derived from a diamine containing aromaticgroup and carboxylic acid group, such that the dissolvable polyimide canbe dissolved in the solvent and cross-linked with the crosslinkingagent. As such, the polyimide composition of the present invention isconvenient for being processed to form a membrane, and a separationmembrane with good processability and resistance to high-polaritysolvent that is useful in PV and VP can be prepared through thepreparation method of separation membrane using the polyimidecomposition according to the present invention.

To make the features and advantages of the present invention clearer andmore comprehensible, the present invention is described in detail belowwith reference to specific embodiments.

DESCRIPTION OF THE EMBODIMENTS

Herein, the range from “one numerical value to another numerical value”is a summary notation by which all numerical values in the range areavoided to be enumerated in the specification. Therefore, reference to aparticular numerical range encompasses any numerical values within thatrange and smaller numerical ranges defined by any numerical valueswithin that range, as if any of the numerical values and the smallerranges of numerical values are expressly indicated in the specification.

Herein, the structure of a polymer or a group is sometimes representedby a skeleton formula. In this representation, carbon atoms, hydrogenatoms, and carbon-hydrogen bonds may be omitted. Of course, where theatom or atomic group is expressly drawn in the structural formula, whatis drawn prevails.

To prepare a separation membrane with good resistance to high-polaritysolvent and processability that can be used in PV, the present inventionprovides a polyimide composition, and a preparation method of separationmembrane using the polyimide composition. The separation membraneprepared through the preparation method of separation membrane canachieve the above advantages. Hereinafter, the polyimide composition,and the preparation method of separation membrane of the presentinvention are described in detail with reference to embodiments, basedon which the present invention can be practiced.

[Polyimide Composition]

A polyimide composition according to an embodiment of the presentinvention includes a dissolvable polyimide, a crosslinking agent, and asolvent.

In this embodiment, the dissolvable polyimide is represented by formula1:

In formula 1, B is a tetravalent organic group derived from atetracarboxylic dianhydride containing aromatic group. That is to say, Bis a residue in the tetracarboxylic dianhydride containing aromaticgroup other than the two 2 carboxylic dianhydride groups (—(CO)₂O).Herein, the tetracarboxylic dianhydride containing aromatic group isalso referred to as dianhydride monomer.

Particularly, in this embodiment, B is

That is to say, the tetracarboxylic dianhydride containing aromaticgroup (that is, dianhydride monomer) may be bis-(3-phthalyl anhydride)ether (ODPA), 1,2,4,5-benzenetetracarboxylic anhydride (PMDA),4,4′-(hexafluoro-isopropylidene) diphthalic anhydride (6FDA),3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), or3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA).

In formula 1, A is a divalent organic group derived from a diaminecontaining aromatic group, and A′ is a divalent organic group derivedfrom a diamine containing aromatic group and carboxylic acid group. Thatis to say, A and A′ are respectively a residue in the diamine compoundother than the 2 amino groups (—NH₂). Herein, the diamine containingaromatic group, and the diamine containing aromatic group and carboxylicacid group are both referred to as diamine monomers. From another pointof view, in this embodiment, plural diamine monomers need to be used forpreparing the dissolvable polyimide represented by formula 1.

Particularly, in this embodiment, A is

That is to say, the diamine containing aromatic group (that is, diaminemonomer) may be 2,2-bis [(4-aminophenoxy) phenyl] propane (BAPP),2,2′-bis(methyl)benzidine (DMB), 2,2′-bis(trifluoromethyl)benzidine(TFMB), 4,4′-(9-fluorenylidene)dianiline (FDA), 4,4′-diaminodiphenylether, p-phenylenediamine, m-phenylenediamine, 2,4′-diaminodiphenylether or 1,3-bis-4-aminophenoxybenzene (TPE-R).

Further, in this embodiment, A′ is

That is to say, the diamine containing aromatic group and carboxylicacid group (that is, diamine monomer) may be 3,5-diaminobenzoic acid(DABA), 3,4-diaminobenzoic acid, 5,5′-methylenebis(2-amino-benzoic-acid) (MBA), or other diamines bearing a carboxylicacid functional group.

In formula 1, 0.1≤X≤0.9, and preferably 0.3≤X≤0.7.

Moreover, the dissolvable polyimide represented by formula 1 is obtainedthrough an imidization reaction of the dianhydride monomer and thediamine monomers. In particular, the imidization takes place in asolvent through any method well known to those skilled in the art. Thesolvent is not particularly limited, as long as it can dissolve thedianhydride monomer and the diamine monomers. In this embodiment, thesolvent includes, but is not limited to: N-methyl-2-pyrrolidone (NMP),N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO),dimethylformamide (DMF), hexamethylphosphoramide, m-cresol or acombination thereof. In addition, the imidization ratio of theimidization reaction is 100%. In addition, in an embodiment, B informula 1 is

A in formula 1 is

and A′ in formula 1 is

That is, the dissolvable polyimide represented by formula 1 in thisembodiment is obtained through an imidization reaction of ODPA, BAPP,and DABA.

Notably, the inventors find that the polyimide can be dissolved in asolvent (described in detail hereinafter) by comprising a divalentorganic group derived from a diamine containing aromatic group, and thepolyimide can be crosslinked with a crosslinking agent (described indetail hereinafter) by comprising a divalent organic group derived froma diamine containing aromatic group and carboxylic acid group. As aresult, in this embodiment, the dissolvable polyimide represented byformula 1 can be dissolved in the solvent (described in detailhereinafter) and crosslinked with the crosslinking agent (described indetail hereinafter) by comprising a specific ratio of the divalentorganic group derived from a diamine containing aromatic group and thedivalent organic group derived from a diamine containing aromatic groupand carboxylic acid group.

In this embodiment, the crosslinking agent may be an aziridinecrosslinking agent, an isocyanate crosslinking agent, an epoxycrosslinking agent, a diamine crosslinking agent or a triaminecrosslinking agent. In particular, in this embodiment, the crosslinkingagent can be crosslinked with the carboxylic acid group contained in thedivalent organic group derived from a diamine containing aromatic groupand carboxylic acid group in the dissolvable polyimide represented byformula 1, at a temperature ranging from 15 to 100° C.

Particularly, in this embodiment, the aziridine crosslinking agent mayinclude:

the isocyanate crosslinking agent is, for example, but not limited to:diphenyl-methane diisocyanate (MDI) or toluene diisocyanate (TDI); thediamine crosslinking agent is, for example, but not limited to:ethylenediamine, hexylenediamine or p-phenylenediamine; and the triaminecrosslinking agent is, for example, but not limited to: triethylamine.

In this embodiment, the solvent is not particularly limited, as long asit can dissolve the dissolvable polyimide and the crosslinking agent. Inparticular, in this embodiment, the solvent includes, but is not limitedto: N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), dimethylformamide (DMF) or a combination thereof.

Furthermore, in this embodiment, based on the total weight of thepolyimide composition, the content of the dissolvable polyimide is 5 to25 wt %, and preferably 8 to 20 wt %; and the content of thecrosslinking agent is 1 to 15 wt %, and preferably 1 to 10 wt %. Inparticular, if the content of the dissolvable polyimide is lower than 5wt %, the strength of the membrane is poor; and if the content of thedissolvable polyimide is higher than 25 wt %, the processability ispoor. If the content of the crosslinking agent is lower than 1 wt %, thedegree of crosslinking is insufficient; and if the content of thecrosslinking agent is higher than 15 wt %, the processability is poor.

Notably, as described above, by comprising a specific ratio of thedivalent organic group derived from a diamine containing aromatic groupand the divalent organic group derived from a diamine containingaromatic group and carboxylic acid group, the dissolvable polyimiderepresented by formula 1 can be dissolved in the solvent and crosslinkedwith the crosslinking agent. As a result, by including the dissolvablepolyimide, the crosslinking agent, and the solvent, the polyimidecomposition is convenient for being processed to form a membrane, andthe membrane prepared with the polyimide composition has porosity andgood resistance to high-polarity solvent.

Further, the polyimide composition having the above advantages is usefulin the preparation of a separation membrane for use in a separationprocess.

[Preparation Method of Separation Membrane]

The preparation method of separation membrane according to an embodimentof the present invention includes the following steps. First, apolyimide composition according to any one of the above embodiments isprovided. In particular, the polyimide composition is prepared byuniformly mixing a dissolvable polyimide with a crosslinking agent in asolvent at a temperature ranging from 15 to 100° C. The mixing method isnot particularly limited, as long as the dissolvable polyimide can beuniformly mixed with the crosslinking agent in the solvent to facilitatethe progression of the crosslinking process (described in detailhereinafter). Moreover, the polyimide composition and the componentstherein have been described in detail in the foregoing embodiments, andthus are not described here again.

Then, a crosslinking process is performed on the polyimide composition.In particular, the carboxylic acid group contained in the divalentorganic group derived from a diamine containing aromatic group andcarboxylic acid group in the dissolvable polyimide is cross-linked withthe crosslinking agent in this step, so as to form a polyimide having acrosslinked structure. More particularly, in this embodiment, theduration of the crosslinking process is from 1 to 8 hours, and thetemperature of the crosslinking process is in the range of 15 to 100°C., and preferably 50 to 80° C.

Next, the polyimide composition which has been subjected to thecrosslinking process is coated on a substrate to form a polyimidemembrane. In this step, the substrate is not particularly limited, aslong as it can support the polyimide membrane. Particularly, thesubstrate is, for example, a polyester nonwoven fabric or apolypropylene nonwoven fabric. Moreover, in this step, the coatingmethod includes, but is not limited to: doctor blade coating, wire barcoating, or screen printing. Furthermore, in this embodiment, thethickness of the polyimide membrane is from 1 to 50 μm.

Then, a dry phase inversion process is performed on the polyimidemembrane, so as to obtain a separation membrane. In this embodiment, thedry phase inversion process includes a step of vaporizing the solvent inthe polyimide membrane completely at a constant temperature under aninert atmosphere. That is to say, in this embodiment, the separationmembrane is a dense membrane.

More particularly, in this embodiment, the temperature of the dry phaseinversion process is from 50 to 80° C.

Furthermore, after the polyimide membrane is contacted with the ambientmoisture, mass transfer and exchange may take place between a part ofthe solvent in the polyimide membrane and the moisture, such that a partof polyimide is precipitated out, and wet phase inversion takes place.Therefore, in the preparation method of separation membrane, after thepolyimide composition is coated onto the substrate to form a polyimidemembrane, the dry phase inversion step is performed immediately toobtain a separation membrane suitable for use in PV and VP.

Notably, as described above, the separation membrane prepared with thepolyimide composition according to any one of the embodiments aboveafter the crosslinking process, the coating process, and the dry phaseinversion process has good processability, resistance to high-polaritysolvent, and porosity. Further, as can be known from above, theseparation membrane has a dense structure and thus the separationmembrane prepared through the preparation method of separation membraneaccording to this embodiment can be used in PV and VP.

The features of the present invention will be described in furtherdetail below with reference to Examples 1 to 3. Although the followingexamples are described, the materials used, their amounts and ratios,details and processes of treatments, etc., may be appropriately variedwithout departing from the scope of the present invention. Accordingly,the present invention should not be construed to be limited to theexamples set forth hereinafter.

Example 1

Preparation of Dissolvable Polyimide

First, the diamine monomers BAPP and DABA were dissolved at a fixedmolar ratio in an organic solvent dimethylacetamide (DMAc) orN-methylpyrrolidone (NMP). After complete dissolution, a dianhydridemonomer ODPA was added for polycondensation, and a high-viscositypoly(amic acid) solution was formed, wherein the molar ratio of themonomers in reaction was BAPP:DABA:ODPA=5:5:10. Then, the poly(amicacid) was cyclized to form a dissolvable polyimide of Example 1. Thedianhydride monomer was not limited to ODPA and BPDA, and the diaminemonomer containing carboxylic acid group was not limited to DABA. Themolar ratio of the monomers in reaction was BAPP:DABA:dianhydridemonomer=5:5:10, 7:3:10 or 9:1:10.

Preparation of Polyimide Composition

15 g of the dissolvable polyimide prepared in Example 1, 5 g of anaziridine crosslinking agent, and 80 g of the solvent NMP were added toa 100 mL flask fitted with a mechanical stirrer, and stirred for 0.5hours at 30° C. under a nitrogen atmosphere, so as to uniformly mix thedissolvable polyimide of Example 1 with the aziridine crosslinking agentin the solvent NMP. In this way, the polyimide composition of Example 1was obtained.

Preparation of Separation Membrane

The polyimide composition of Example 1 was coated onto a polyesternonwoven fabric or a polypropylene nonwoven fabric (that is, thesubstrate) by doctor blade coating at 30° C. under a nitrogenatmosphere, so as to form a polyimide membrane of 5 μm in thickness.Subsequently, a dry phase inversion process was immediately performed onthe polyimide membrane by drying it in an oven at 80° C., so as toobtain a separation membrane of Example 1.

Example 2

Preparation of Dissolvable Polyimide

A dissolvable polyimide of Example 2 was prepared following the samepreparation process as that in Example 1.

Preparation of Polyimide Composition

A polyimide composition of Example 2 was prepared following the samepreparation process as that in Example 1, except that the contents ofthe components in the polyimide composition of Example 2 were notabsolutely the same as that in the polyimide composition of Example 1,as shown in Table 1.

Preparation of Separation Membrane

The separation membrane of Example 2 was prepared following the samepreparation process as that in Example 1, except that the polyimidecomposition of Example 2 was used.

Example 3

Preparation of Dissolvable Polyimide

A dissolvable polyimide of Example 3 was prepared following the samepreparation process as that in Example 1.

Preparation of Polyimide Composition

A polyimide composition of Example 3 was prepared following the samepreparation process as that in Example 1, except that the contents ofthe components in the polyimide composition of Example 3 were notabsolutely the same as that in the polyimide composition of Example 1,as shown in Table 1.

Preparation of Separation Membrane

The separation membrane of Example 3 was prepared following the samepreparation process as that in Example 1, except that the polyimidecomposition of Example 3 was used.

TABLE 1 Example 1 Example 2 Example 3 Dissolvable polyimide (wt %) 15 1515 Aziridine crosslinking agent (wt %) 5 10 12.5 NMP (wt %) 80 75 72.5

Then, the solvent resistance test, and the measurements of thepermeation flux and the water concentration in permeate were performedon the separation membranes of Examples 1-3. The above-mentionedmeasurements are illustrated below. The results of the permeation fluxand the water concentration in permeate are shown in Tables 2 to 4.

<Solvent Resistance Test>

The separation membranes of Examples 1-3 were placed in the solvent NMPfor 24 hours, and observed. The results show that the cross-linkedseparation membranes of Examples 1-3 are not back dissolved in thesolvent NMP. That is, the separation membranes of Examples 1-3 have goodstability against NMP.

<Measurement of Permeation Flux and Water Concentration in Permeate>

The separation membranes of Examples 1-3 were placed in a flat membranepervaporation apparatus respectively to carry out pervaporation. Inparticular, during the pervaporation, the operation temperature was 25°C., the feed solution was contacted in liquid form with the outersurface of the separation membrane, the pressure at the downstream sidewas maintained at 3 to 5 mmHg by means of a vacuum pump, thereby forminga pressure difference that allows the feed solution to permeate theseparation membrane as a gas, and leave from the internal surface. Thegaseous material leaving the internal surface was condensed with liquidnitrogen and collected at the downstream side.

The permeation flux is calculated by an equation below:

$P = {\frac{W}{A \times t}( {g\text{/}m^{2}h} )}$

wherein P, W, A and t are respectively the permeation flux (g/m² h),permeation weight (g), active area on the outer surface of theseparation membrane (m²), and operation time (h).

The water concentration in permeate is obtained by detecting thecondensed and collected material at the downstream side by gaschromatography (GC).

Particularly, in an experiment, the feed solution is a 50 wt % NMPsolution in water. The permeation flux and the water concentration inpermeate of the separation membrane in Example 3 are shown in Table 2.In another experiment, the feed solution is a 90 wt % NMP solution inwater, and the permeation flux and the water concentration in permeateof the separation membranes in Examples 1-3 are shown in Table 3. In afurther experiment, the feed solutions are a 70 wt % isopropanol (IPA)solution, a 90 wt % IPA solution, a 70 wt % ethanol (EtOH) solution anda 90 wt % EtOH solution, and the permeation flux and the waterconcentration in permeate of the separation membrane in Example 3 areshown in Table 4.

TABLE 2 50 wt % NMP Example 1 Example 2 Example 3 Permeation flux(g/m²h) — — 339.11 Water concentration in — — 100 permeate (wt %)

TABLE 3 90 wt % NMP Example 1 Example 2 Example 3 Permeation flux(g/m²h) 90.55 158.62 160.32 Water concentration in 98.1 99.1 100permeate (wt %)

TABLE 4 70 wt % 90 wt % 70 wt % 90 wt % Example 3 IPA IPA EtOH EtOHPermeation flux 2060.50 1185.21 2024.44 1033.93 (g/m²h) Water 99.4 99.999.8 99.8 concentration in permeate (wt %)

It can be known from Tables 2 to 4 that the separation membranes ofExamples 1-3 all have good resistance to high-polarity solvents,permeation flux, and water concentration in permeate. Therefore, theseparation membranes of Examples 1-3 are suitable for use in PV and VP.

The present invention has been described by way of examples; however,the present invention is not limited thereto. Various changes andmodifications may be made by those skilled in the art without departingfrom the spirit and protection scope of the present invention as definedby the appended claims.

What is claimed is:
 1. A polyimide composition, used in a preparationmethod of a separation membrane, comprising: a dissolvable polyimide,represented by formula 1:

wherein B is a tetravalent organic group derived from a tetracarboxylicdianhydride containing aromatic group, A is a divalent organic groupderived from a diamine containing aromatic group, A′ is a divalentorganic group derived from a diamine containing aromatic group andcarboxylic acid group, and0.1≤X≤0.9; a crosslinking agent, wherein the crosslinking agent is anaziridine crosslinking agent, an isocyanate crosslinking agent, an epoxycrosslinking agent, a diamine crosslinking agent, or a triaminecrosslinking agent; and a solvent, wherein the preparation method of theseparation membrane comprises performing a crosslinking process on thepolyimide composition, and a temperature of the crosslinking process isfrom 15 to 30° C.
 2. The polyimide composition according to claim 1,wherein B is


3. The polyimide composition according to claim 1, wherein B is

A is

and A′ is


4. The polyimide composition according to claim 1, wherein the aziridinecrosslinking agent comprises:


5. The polyimide composition according to claim 1, wherein based on atotal weight of the polyimide composition, a content of the dissolvablepolyimide is 5 to 25 wt %, and a content of the crosslinking agent is 1to 15 wt %.